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During cell division, peroxisomes are inherited to daughter cells but some are retained in the mother cells. Our knowledge on how peroxisome inheritance and retention is balanced and how this is regulated for each individual organelle remains incompletely understood. The new findings by Knoblach et al (2013) published in this issue of The EMBO Journal demonstrate that Inp1p functions as a bridging protein to connect ERresident Pex3p and peroxisomal Pex3p, which anchors peroxisomes to the cortical ER for organelle retention in the mother cell. Asymmetric peroxisome division generates peroxisomes, which lack Inp1p but contain Inp2p instead, and only these peroxisomes are primed for myosin-driven transport to daughter cells. Peroxisomes are single membrane-bound organelles found in almost all eukaryotic cells. They harbour a wide spectrum of metabolic activities that vary among different species, developmental stages and cell types (Schlüter et al, 2010). Eukaryotic cells have evolved elaborate mechanisms to ensure the maintenance of peroxisomes. New peroxisomes can form either de novo by budding from the ER or by growth and division of pre-existing organelles (Lazarow and Fujiki, 1985; Hoepfner et al, 2005). Despite the fact that peroxisomes can form de novo, yeast favours to multiply peroxisomes by growth and division (Motley and Hettema, 2007). It therefore has to be ensured that both mother and daughter cells get their share of peroxisomes during cell division. Thus, some peroxisomes need to be retained in the mother cell, while other peroxisomes are directed for transport and inheritance to daughter cells. Both processes have to be balanced to ensure a successful distribution of the organelles between the mother cell and the newly formed bud. The molecular details of how an even peroxisome distribution of dividing cells are maintained have now been disclosed by Knoblach et al (2013), advancing an exciting scientific journey. This journey originally started by the finding that the partitioning of peroxisomes between mother cell and bud is dependent on actin filaments and the myosin motor protein Myo2p (Hoepfner et al, 2001). Inp1p and Inp2p were identified by the Rachubinski group and Inp2p turned out to function as the peroxisomal tether, which interacts with Myo2p and hooks the organelle onto the actin-track on the road to the bud (Fagarasanu et al, 2006). Inp1p was shown to be a peripheral peroxisomal membrane protein, which acts as a peroxisome-retention factor, tethering peroxisomes to putative anchoring structures within the mother cell and bud (Fagarasanu et al, 2005). Later on, Pex3p, a multifunctional protein of the peroxisomal life cycle, was identified as peroxisomal membrane anchor of Inp1p (Munck et al, 2009). Until now, it was therefore known that peroxisomes hook onto Inp1p by Pex3p and Inp1p connects peroxisomes to cortical structures of unknown nature. Thus, it was an open question how peroxisomes are trapped in the mother cell and which additional factors are required for this process. The work of Knoblach et al (2013) published in this issue of The EMBO Journal now unravelled this mystery, allowing for a more complete picture of the whole process of peroxisome retention and inheritance (Figure 1A). The authors show that peroxisomes are recruited to mitochondria that artificially expose Inp1p on their surface, clearly demonstrating that Inp1p acts as a peroxisome tether. Most importantly, they identified the mechanism of how peroxisomes are directed and anchored to the cell cortex: the ER acts as a membrane anchor for the retention of peroxisomes during cell division. In vitro binding assays revealed that Inp1p contains two independent binding sites for Pex3p, located at the Cand the N-terminal region of the protein, respectively. Since Pex3p exhibits a dual localization at the peroxisomal membrane and at the ER, Inp1p seems to bind to Pex3p of both compartments in vivo and thus link Pex3p molecules across two membranes. Indeed, it turned out that ER-located Pex3p recruits Inp1p to discrete foci in close proximity to the cortical ER. Using the split-GFP assay, the authors confirmed that Inp1p interacts not only with ER-bound Pex3p but also with Pex3p in the peroxisomal membrane. Thus, the core of the ER-peroxisome tether is generated by the Inp1p-mediated linkage of ER-bound Pex3p with peroxisomal Pex3p. The functional relevance of this ER-peroxisome tether is disclosed by the phenotype of peroxisome inheritance mutants. Accordingly, the Pex3p–V81E mutant, affected in the recruitment of Inp1p to the ER, is characterized by a defect of ER retention of peroxisomes, which drives all peroxisomes into the bud and leaves no peroxisomes in the mother cell (Figure 1B). To piece together the puzzle, a final gap had to be filled. How is the peroxisomal fraction remaining in the mother cell discriminated from those ferried to the bud during cell division? In budding wild-type cells, Inp1p exhibits a striking asymmetry along the cell division axis. Knoblach et al (2013) The EMBO Journal (2013) 32, 2424–2426 www.embojournal.org